bigtable: Ignore empty lines in cbtrc
Empty lines in the .cbtrc config file would lead to a cryptic error
message about an invalid line in the config file when using the cbt
command line tool. This change will make the tool ignore empty lines
in the config file.
Fixes #1679.
Change-Id: I6e4ddeef559a263f0c220281bd6c481908f62bf5
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/48810
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>